1. Field of the Invention
The present invention generally relates to a flat color cathode ray tube, and in particular, to a flat color cathode ray tube with excellent doming quality by improving the structure of a flat panel and by using a shadow mask made of AK (aluminum-killed) material.
2. Description of the Related Art
FIG. 1 is a diagram explaining the structure of an already-known color cathode ray tube.
Referring to FIG. 1, the conventional color cathode ray tube includes a front side glass panel 1, and a rear side glass funnel 2 that is jointed with the panel 1. The panel 1 and the funnel 2 are sealed together in a manner such that their insides are under vacuum, forming a vacuum tube.
A fluorescent screen 13 is formed on the inner side of the panel 1, and an electron gun 8 is mounted in a neck portion of the funnel 2 that opposes the fluorescent screen 13.
A shadow mask 3 for dividing three color electron beams emitted from the electron gun 8, spaced at a given distance away from the fluorescent screen 13. The shadow mask 3 is combined with a mask frame 4, and is elastically supported by a spring 5, and further by the panel 1 with a stud pin 5.
The mask frame 4 is jointed with an inner shield 7 that is made of a magnetic material to reduce any movement of electron beam 11 due to an external magnetic field, particularly from the rear side of the cathode ray tube (or Braun tube).
On the other hand, a convergence purity magnet (CPM) 10 for adjusting R, G, and B electron beams to converge on a point, and a deflection yoke 9 for deflecting the electron beam 11 are mounted on a neck portion of the funnel 2.
Also, a reinforcing band 12 is included to reinforce the front surface glass in order to offset the influence of a vacuum state of the tube.
To explain the operation of a thusly constructed color cathode ray tube, the electron beams 11 emitted from the electron gun 8 are deflected vertically and horizontally by the deflection yoke 9, and the deflected electron beams 11 pass through beam pass holes in the shadow mask 3, and strike the fluorescent screen 13 on the front, consequently displaying designated color images.
Here, the convergence purity magnet 10 compensates the convergence and purity of R, G, and B electron beams 11, and the inner shield 7 blocks the influence of the magnetic field from the rear side of the cathode ray tube.
FIG. 2 is a diagrammatic view explaining a conventional panel and a flat panel.
As depicted in the drawings, FIG. 2a shows a panel, the outside surface of which is substantially flat and the inside surface thereof is has a curvature, while FIG. 2b shows a panel, the outside and inside surfaces of which are all curved.
It has been believed that the panel 1 of the cathode ray tube, on which images are displayed, should be curved both inside and outside in order to withstand the high vacuum state of the inside of the cathode ray tube, and to make the electron beams land easily.
However, external light is severely reflected on the peripheral side rather than at the center of the panel 1 in terms of the incidence angle of the external light, and this consequently makes users see very distorted images on the peripheral side. For such reason, the flat type panel 1 has drawn a lot of interests and in fact, most of panels 1 currently being used tend to be flat as shown in FIG. 2a. 
Korean Patent Laid-Open No. 0282536 discloses a panel in which the outer surface is flat and the inner surface is curved.
As illustrated in FIG. 2a, as for the flat color cathode ray tube including a panel having a flat outer surface and curved inner surface and a frame mask, a shadow mask is further provided as a dichroic means, receiving tension to minimize deterioration of picture quality that often occurs due to a doming phenomenon of the shadow mask.
Keeping abreast of such trend, the curvature of the shadow mask in the panel 1 is also becoming flat similar to that of the panel's inner surface. The panel's inner surface is curved in connection with the dichroic function for images, while the shadow mask is curved for more convenient landing that determines convergence for converging R, G, and B electron beams to one point by deflection and color purity of images.
However, as the inner surface of the shadow mask became flatter, doming, which is thermal deformation of the shadow mask due to the electron beam, became a problem. To solve the problem, a shadow mask made of invar material having a relatively low coefficient of thermal expansion was introduced.
Unfortunately though, a shadow mask made of invar is too expensive, thus increasing the overall production cost.